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@ -364,13 +364,13 @@ Today users of network games often experience failures of the servers while
playing or downtime due to maintenance.
Additionally game developers often perform the difficult task of reinventing
a game server to meet their needs.
The purpose of this thesis is to to design a reliable game server which
can power different types of games simultanously.
The purpose of this thesis is to design a reliable game server which can
power different types of games simultaneously.
\end_layout
\begin_layout Abstract
It is investigated if the techniques and tools used in the telecom industry,
specifically Erlang and the OTP, can be used to create a highly reliable
specifically Erlang and the OTP can be used to create a highly reliable
game server.
To make the server generic, it is investigated if virtual machines can
be used to run the actual games, thereby allowing the games to be developed
@ -507,12 +507,12 @@ Introduction
\end_layout
\begin_layout Standard
Online gaming, and computer gaming in general has become an important part
Online gaming and computer gaming in general has become an important part
in the day-to-day lives of many people.
A few years ago, computer games were not at all as popular as they are
today.
With the advances in computer graphics and computer hardware today's games
are much more sophisticated then they were in the days of
are much more sophisticated than they were in the days of
\emph on
NetHack
\emph default
@ -560,7 +560,7 @@ textbf{NetHack}}{An early computer game developed by the NetHack team, arguably
\end_layout
\begin_layout Standard
The early computer games featured simple, or no graphics at all
The early computer games featured simple or no graphics at all
\begin_inset CommandInset citation
LatexCommand citep
key "nethack:website"
@ -575,11 +575,11 @@ key "nethack:website"
\end_layout
\begin_layout Standard
Since these early games, the gaming industry have become much more influential
Since these early games, the gaming industry has become much more influential
in many ways.
Many advances in computer hardware are thought to come from pressure from
the computer game industry.
More powerful games require more powerful, and more easily available hardware
More powerful games require more powerful and more easily available hardware
\begin_inset Note Note
status collapsed
@ -650,7 +650,7 @@ The idea of game servers is not new, network games have been played for
\emph on
Quake
\emph default
series, or the
series, and the
\emph on
Doom
\begin_inset Note Note
@ -789,8 +789,9 @@ status open
\backslash
nomenclature{
\backslash
textbf{Hardware failiure}}{A failiure in hardware (hard drive, memory, processor
, etc) which causes a system to stop functioning}
textbf{Hardware failure}}{A failure in hardware (hard drive, memory, processor,
etc.) which causes a system to function in a different way than originally
intended, or crash}
\end_layout
\begin_layout Plain Layout
@ -799,8 +800,9 @@ textbf{Hardware failiure}}{A failiure in hardware (hard drive, memory, processor
\backslash
nomenclature{
\backslash
textbf{Software failiure}}{A failiure in software (the GGS, the operating
system, etc) which causes a system to stop functioning}
textbf{Software failure}}{A failure in software (the GGS, the operating
system, etc.) which causes a system to function in a different way than
what was originally intended, or crash}
\end_layout
\end_inset
@ -825,7 +827,7 @@ The game industry is a quickly growing industry with high revenues and many
Strangely enough gamers often experience long downtimes due to maintaining
or because of problems with the servers
\begin_inset CommandInset citation
LatexCommand citet
LatexCommand citep
key "news/cnet/com/WoWProblems"
\end_inset
@ -882,7 +884,7 @@ the nine nines
of availability
\begin_inset CommandInset citation
LatexCommand citet
LatexCommand citep
key "Armstrong03"
\end_inset
@ -905,7 +907,7 @@ s, leaving the public unable to contact emergency services.
\begin_layout Standard
Moving back to the gaming industry.
The main reason to develop reliable servers is a higher revenue for game
The main reason to develop reliable servers is higher revenue for game
companies, to achieve this it is important for game companies to expand
their customer base.
Reliable game servers will create a good image of the company.
@ -969,10 +971,11 @@ key "Bondi:2000:CSI:350391.350432"
.
These two issues are addressed in this thesis.
Structural scalability means expanding an architecture, e.g.
Structural scalability means expanding architecture, e.g.
adding nodes to a system without requiring modification of the system.
Load scalability means using the available resources in a way which allows
handling increasing load, e.g more users, gracefully.
handling increasing load, e.g.
more users, gracefully.
\end_layout
\begin_layout Standard
@ -1023,8 +1026,8 @@ reference "sec:Generic"
\begin_layout Standard
The server behaves in a way similar to an application server, but is designed
to help running games instead pf typical applications.
An application server provides processing ability and time, therefore it
to help running games instead of typical applications.
An application server provides processing ability and time; therefore it
is different from a file- or print-server, which only serves resources
to the clients.
In order to more easily understand the purpose of the GGS, it can be of
@ -1046,11 +1049,21 @@ Glassfish
\emph on
Google App Engine
\emph default
where you can run applications written in Python or some language which
where you can run applications written in Python or any language which
runs in the
\emph on
Java Virtual Machine
\emph default
\begin_inset Note Note
status open
\begin_layout Plain Layout
Reference to app engine
\end_layout
\end_inset
.
An example of an application server not powering web applications, but
instead regular business logic, is Oracle’s
@ -1314,7 +1327,7 @@ Internally the GDL VM needs to interface with the GGS to make use of the
helpers and tools that the GGS provides.
Thus an internal API has to be designed to make the GDL VM be able to interact
with the GGS.
This API is ideally completely independent of the GDL, and reusable for
This API is ideally completely independent of the GDL and reusable for
any GDL.
\end_layout
@ -1340,7 +1353,7 @@ reliable
In order to facilitate scalability the GGS needs a storage platform which
is accessible and consistent.
The scalability aspects of the GGS are discussed from a theoretical point
of view, however no practical implementation of the scalability aspects
of view, however no practical implementations of the scalability aspects
are found in the prototype.
\end_layout
@ -1386,7 +1399,7 @@ The UDP protocol is not supported for communication between client and server.
ation process using TCP was faster and easier than if UDP would have been
used.
UDP is generally considered to be faster than TCP for the transfer of game
(and other) related data, this is discussed in more depth in
(and other) related data; this is discussed in more depth in
\begin_inset CommandInset ref
LatexCommand vref
reference "sec:Choice-of-network"
@ -1394,7 +1407,7 @@ reference "sec:Choice-of-network"
\end_inset
.
In short, the decision of using TCP means that games that requires a high
In short, the decision of using TCP means that games that require a high
speed protocol will not be supported by the GGS prototype.
Another limitation necessary to set on the system is the possibility to
have huge game worlds due to the implementation of the scaling mechanism
@ -1455,7 +1468,7 @@ World of Warcraft
\begin_layout Standard
In turn based games each player has to wait for their turn.
Latency is not a problem since the gameplay does not require fast interactions
among the players, long round trip times will not be noticed.
among the players; long round trip times will not be noticed.
Examples of turn based games include board and card games, as well as multiplay
er games like
\emph on
@ -1508,11 +1521,11 @@ textbf{Module}}{A part of a larger system}
\end_layout
\begin_layout Standard
The first prototype of the GGS consisted of simple modules, however, due
The first prototype of the GGS consisted of simple modules; however, due
to the separation of concerns among the modules, they were easily independently
modified and improved.
Once the basic structure of the GGS had been established, the first prototype
was removed, remaining was the structure of the modules and the internal
was removed; remaining was the structure of the modules and the internal
flow of the application.
This could be seen as an iterative workflow, with the first prototype being
the first iteration.
@ -1551,7 +1564,7 @@ name "cha:Theory"
\begin_layout Standard
In this chapter, the theory behind the techniques used in the GGS are discussed.
Performance issues and the measuring of performance is discussed.
Performance issues and the measuring of performance are discussed.
Benchmarking techniques are discussed.
The options when choosing network protocols are given, along with a discussion
of each alternative.
@ -1601,7 +1614,7 @@ Chess club
- a building where chess players can meet and play chess.
In the following text the choice of using a chess club for modeling the
GGS is discussed.
The chess club is described in greater detail, furthermore the corresponding
The chess club is described in greater detail; furthermore the corresponding
parts of the chess club in the GGS are described.
Since a real-world scenario is readily available, and to such a large extent
resembles the computer software required for the GGS, the next step in
@ -2270,10 +2283,6 @@ status open
Performance measurements
\end_layout
\begin_layout Plain Layout
\end_layout
\begin_layout Plain Layout
Tue apr 26, 9:15.
Continue from here on.
@ -2380,7 +2389,7 @@ name "sec:Choice-of-network"
\begin_layout Standard
There are two main types of protocols with help of which computer communication
over the Internet usually takes place; TCP and UDP which are known as the
over the Internet usually takes place, TCP and UDP which are known as the
network layer protocols and HTTP which is the most prominent application
layer protocol.
The transport layer protocols are commonly used to transport application
@ -2538,11 +2547,12 @@ name "sec:Generic"
The GGS is a game server.
It was made with a desire to be suitable for many kinds of games.
A game should not only be able to vary in terms of genre, graphics, gameplay
etc, but also in the way the game is implemented for example in different
programming languages.
etc.
but also in the way the game is implemented for example in different programmin
g languages.
The GGS should be OS independent and run on Windows, OS X and Linux.
The GGS can be run as a listen server on the players computer and host
games locally.
The GGS can be run as a listen server on the computers of the players and
host games locally.
It could also be a dedicated server running on dedicated independent hardware.
It is meant to run any game in any environment in any way desired, therefore
being as generic as possible.
@ -2551,7 +2561,7 @@ The GGS is a game server.
\begin_layout Standard
Clients upload the source code of the game it would like to play on the
GGS, this way any client can connect to the server and install the game
through a API without the need of installation through the server provider
through an API without the need of installation through the server provider
or maintainer.
\end_layout
@ -2671,14 +2681,14 @@ name "sec:Availability"
\begin_layout Standard
One important factor of any server is the availability.
A server which is unreachable is an useless server.
A server which is unreachable is a useless server.
\end_layout
\begin_layout Standard
Within the telecom sector high availability has been achieved
\begin_inset CommandInset citation
LatexCommand citet
LatexCommand citep
key "armstrong2011"
\end_inset
@ -2692,7 +2702,7 @@ key "armstrong2011"
There are several good papers (e.g.
\begin_inset CommandInset citation
LatexCommand citet
LatexCommand citep
key "VM:Jin2010,VM:Polze"
\end_inset
@ -2700,7 +2710,7 @@ key "VM:Jin2010,VM:Polze"
) on how to migrate whole virtual machines among nodes to replicate them
but for the GGS a different approach has been chosen.
Instead of duplicating a virtual machine, an attempt to lift the state
of the VM to a storage external to the VM is made.
of the VM to storage external to the VM is made.
The state is stored in a fast, fault tolerant data store instead of inside
the VM.
In addition to migrating the state of the game VM, the GGS uses tools from
@ -2732,7 +2742,8 @@ status open
\backslash
nomenclature{
\backslash
textbf{Supervisor}}{A process monitoring and hadning crashes in other processes}
textbf{Supervisor}}{A process monitoring and handling crashes in other processes
}
\end_layout
\end_inset
@ -3231,7 +3242,7 @@ status open
nomenclature{
\backslash
textbf{Network split}}{Separation of two networks, occurs when two networks
cannot communicate, commonly because of a hardware or software failiure}
cannot communicate, commonly because of a hardware or software failure}
\end_layout
\end_inset
@ -3379,7 +3390,7 @@ JavaScript is a prime GDL candidate for the GGS.
\end_layout
\begin_layout Standard
JavaScript, as a interpreted script language, has gained a lot of popularity
JavaScript, as an interpreted script language, has gained a lot of popularity
in other fields of computer science lately.
It is used as a server side language in large projects such as
\emph on
@ -3602,7 +3613,7 @@ Pong
\emph default
, a game in which two players play a game involving a ball and two paddles.
The goal for each player is to shoot beside the other players paddle while
not allowing the ball to pass by her own paddle.
not allowing the ball to pass by player's own paddle.
The game requires real time updates and is demanding when played in several
instances concurrently.
\end_layout
@ -3647,7 +3658,7 @@ reference "chap:Results-and-discussion"
for each player.
Due to lack of hardware, not enough player processes could be started in
this way.
The bots were rewritten in Erlang, and due to Erlang's light weigh threads,
The bots were rewritten in Erlang, and due to Erlang's light weight threads,
enough processes could have been created to test the server successfully.
\end_layout
@ -3703,7 +3714,7 @@ Overview of the prototype
The prototype of the GGS was developed using the Erlang language.
In Erlang, most things are processes.
The software running the Erlang code is known as the Erlang machine, or
a Erlang node.
an Erlang node.
Each Erlang node is capable of running several
\emph on
threads
@ -3755,7 +3766,7 @@ nomenclature{
\backslash
textbf{Context switch}}{The act of switching from one context, commonly
a process, to another.
Used by operating systems to achieve multi tasking}
Used by operating systems to achieve multi-tasking}
\end_layout
\end_inset
@ -3900,8 +3911,8 @@ reference "fig:The-layout-of"
the entire GGS system is represented graphically.
The circles marked with 'C' topmost in the picture represent game clients.
These circles represent processes running on gamers computers, and not
on the GGS machine.
These circles represent processes running on the computers of the gamers,
and not on the GGS machine.
If a game of chess is to be played on the server, the clients on the machines
of the gamers will be chess game clients.
Clients connect through a network, pictured as a cloud, to the dispatcher
@ -4748,14 +4759,14 @@ The GGS protocol is modeled after the HTTP protocol.
with HTTP due to its presence in internet software.
Each GGS protocol packet contains a headers section.
The headers section is followed by a data section.
In the headers section, parameters concerning the packet is placed.
In the headers section, parameters concerning the packet are placed.
In the data section, the actual data payload of the packet is placed.
\end_layout
\begin_layout Standard
There is no requirement of any specific order of the parameters in the headers
section, however the data section must always follow directly after the
headers section separated by a empty new line.
headers section separated by an empty new line.
\end_layout
\begin_layout Standard
@ -4789,7 +4800,7 @@ The parser of the GGS protocol implemented in the GGS prototype is designed
\end_layout
\begin_layout Standard
Line 4 is a empty line which is, like in the HTTP protocol, the separator
Line 4 is an empty line which is, like in the HTTP protocol, the separator
between the head and body or payload section.
\end_layout
@ -5153,12 +5164,12 @@ Game data from all games on the GGS is stored in the database backend of
\begin_layout Standard
In the GGS prototype the database module is using a database management
system called Mnesia .
system called Mnesia.
Mnesia ships with the standard Erlang distribution and is a key-value store
type of database.
Mnesia is designed to handle the stress of telecoms systems
Mnesia is designed to handle the stress of telecoms systems
\begin_inset CommandInset citation
LatexCommand citet
LatexCommand citep
key "667766"
\end_inset
@ -5244,9 +5255,9 @@ localStorage
localStorage
\noun default
.
To store a value within the database, not only is the table token and the
name of the namespace required, but a unique key so that the value can
be successfully retrieved or modified later.
To store a value within the database, not only are the table token and
the name of the namespace required, but a unique key so that the value
can be successfully retrieved or modified later.
The key is decidable by the game developer.
\end_layout
@ -5265,7 +5276,7 @@ key "webstorage:website"
\end_inset
.
Usage of the web storage standard in the GGS provides a well documented
Usage of the web storage standard in the GGS provides a well-documented
interface to the database backend.
\end_layout
@ -6102,8 +6113,8 @@ key "Savor:1997:HSA:851010.856089"
There are several approaches to a supervisor design in general (when not
just considering how they work in Erlang).
One common approach is to have the supervisor look in to the state of the
process(es) it supervises, and let the supervisor makes decisions based
on this state.
process or processes it supervises, and let the supervisor makes decisions
based on this state.
The supervisor has a specification of how the process it supervises should
function, this is how it makes decisions.
@ -6429,16 +6440,16 @@ The entire GGS was not tested using QuickCheck, nor was the entire client
\begin_layout Standard
QuickCheck has features to generate very large and complex tests, the results
of which can be hard to analyze.
The solution to reading these complex test is to extract a
The solution to reading these complex tests is to extract a
\emph on
minimal failing test case
\emph default
which contains the smallest failing test sequence.
By applying a very large test and gradually simplifying the test to find
the smallest failing sequence, many bugs which would other wise have been
the smallest failing sequence, many bugs which would otherwise have been
hard to catch can be caught
\begin_inset CommandInset citation
LatexCommand citet
LatexCommand citep
key "Arts:2006:TTS:1159789.1159792"
\end_inset
@ -6448,7 +6459,7 @@ key "Arts:2006:TTS:1159789.1159792"
\begin_layout Standard
QuickCheck was originally made for the programming language Haskell.
There is a lot of reimplementations of QuickCheck in various programming
There are a lot of implementations of QuickCheck in various programming
languages.
Erlang QuickCheck (EQC) and Triq are two variants of QuickCheck for Erlang.
EQC was chosen for testing the GGS.
@ -6465,15 +6476,9 @@ In order to test the robustness of the GGS several different artificial
users, so called bots, have been implemented.
Each of these bots is programmed to play a game on the GGS as similar to
a real user as possible.
In the game Pong for example, the bot watches the ball and moves its pad
up or down according to the position of the ball.
For the GGS there is no difference in serving a real user or a bot.
\end_layout
\begin_layout Standard
With help of this method, large amounts of players can be simulated playing
games on the GGS simultaneously, which is a good stress and concurrency
test for the overall system.
A large amount of players can be simulated playing games on the GGS simultaneou
sly, which is a good stress and concurrency test for the overall system.
In section
\begin_inset CommandInset ref
LatexCommand ref
@ -6485,6 +6490,52 @@ reference "sec:Statistics"
bots playing games is being presented.
\end_layout
\begin_layout Subsubsection
Pong
\end_layout
\begin_layout Standard
Pong is a classic video game released by Atari.
Being a real-time based game, the game state will be constantly broadcasted
to all the players of a started Pong game in the GGS.
Each time a Pong game has been started and two bots has joined to play,
there should be clearly observable that the number of messages sent from
the server per second has increased and be stable until a later Pong game
has been started with two bots playing.
If the game would have been turn-based, then the game state would only
be broadcasted when a bot has made a turn.
The time for a bot to make a turn would depend on the complexity of the
current situation of the game.
Because of the current situation varies as the game progress, also the
time between each broadcasted game state varies throughout the game.
This would make the observations during the robustness test say more about
the game than the GGS.
\end_layout
\begin_layout Standard
Pong is a game that consists of two pads and a ball.
Each paddle is controlled by a player and the objective of the game is
to keep the ball between the two pads.
If the ball reaches the opposite side of a players pad then that player
loses while the other player scores.
The ball is displayed in the game as a dot and each pad as a short vertical
line.
The pad can only go straight up or straight down.
The ball moves with constant speed in one direction and never changes its
heading before it reaches a pad or the boundary of the game area.
\end_layout
\begin_layout Standard
The logic of the bots in the Pong game can be simple and still behave realistic
by watching the ball and moving its pad up or down according to the position
of the ball.
In this way the game logic can be evaluated in constant time so that it
doesn't have a bad effect while measuring robustness.
\end_layout
\begin_layout Section
Case studies
\end_layout
@ -6555,12 +6606,11 @@ ed Erlang tuple.
\end_layout
\begin_layout Enumerate
The protocol parser sends this Erlang touple back to the player process.
The protocol parser sends this Erlang tuple back to the player process.
\end_layout
\begin_layout Enumerate
The player process checks if the command is is a Server-Command or a Game-Comman
d.
The player process checks if the command is a Server-Command or a Game-Command.
In our example it is a Game-Command and it sends the message to the table
process.
\end_layout
@ -6770,8 +6820,8 @@ The generic nature of the GGS leaves it up to the client to define which
\end_layout
\begin_layout Standard
The first client which connects to a table is responsible to provide the
JavaScript server source code.
The first client who connects to a table is responsible to provide the JavaScrip
t server source code.
To do so there is a
\noun on
define
@ -7514,7 +7564,7 @@ erlv8
\begin_layout Standard
erlv8 is powered by the V8 engine developed by Google.
The ability to communicate from JavaScript to Erlang using NIF callbacks
is is present in the erlv8 bindings and can be used within the GGS.
is present in the erlv8 bindings and can be used within the GGS.
\end_layout
\begin_layout Standard
@ -7557,7 +7607,7 @@ Protocol design
\end_layout
\begin_layout Standard
Initially the GGS protocol was planed to use the UDP protocol as a transport
Initially the GGS protocol was planned to use the UDP protocol as a transport
layer.
Due to the lack of error checking in the UDP protocol, the UDP protocol
is faster than the TCP protocol, this was a main reason in the desire to
@ -7707,7 +7757,7 @@ Testing of the GGS took place in two separate sessions.
\end_layout
\begin_layout Standard
Each of the two simulations use JavaScript as the GDL.
Each of the two simulations uses JavaScript as the GDL.
The JavaScript is run through Google V8.
The database module uses Mnesia.
\end_layout
@ -7801,7 +7851,7 @@ In the first test, in which Mnesia has been heavily used, the server had
load.
In the next testing session, the test has been conducted with another client
that did not use Mnesia.
Without mnesia the server peaked at 60,000 messages per second, however
Without Mnesia the server peaked at 60,000 messages per second, however
this was only for a very short time.
The average throughput was around 25,000 messages per second, five times
more than what the server was able to process with Mnesia in place.
@ -8199,6 +8249,26 @@ textbf{ETS}}{Erlang Term Storage}
\end_layout
\begin_layout Subsubsection
Integration with existing games
\end_layout
\begin_layout Standard
It should be possible to integrate the GGS with existing network games.
In order to integrate the GGS with an existing game it is neccessary to
1) rewrite the entire server logic in a GDL and deploy this implementation
on the GGS, and 2) write a protocol parser for the protocol of the game
at hand.
\end_layout
\begin_layout Standard
No implementation of a game server for an existing game has been done, however
preliminary investigations on running an early version of Quake on he GGS
have been made.
An interesting future improvement of the GGS would be to develop an implementat
ion of a game server for an existing game for the GGS.
\end_layout
\begin_layout Chapter
Conclusion
\end_layout
@ -8212,7 +8282,7 @@ This thesis describes a method to create a reliable and generic game server
To make the GGS as generic as possible separation of game and server logic
is necessary.
Designing a good API is vital in order to allow game developers to interact
with the server in a easy manner and with minimal overhead.
with the server in a simple manner and with minimal overhead.
Furthermore every game should be isolated so that games can not interfere
with each other.
Isolation can be achieved by introducing a context for each game which

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